Robert A. Cryan

Performance evaluation of optically pre-amplified PPM systems

An original analysis is presented for an optical fiber n-ary pulse position modulation (PPM) system employing optical preamplification. The theoretical results, from calculations performed at a bit-rate of 622 Mbit/s and a wavelength of 1.53 /spl mu/m, demonstrate that the PPM system offers a 7.5 dB sensitivity benefit in comparison with an equivalent PCM system. Furthermore the results illustrate that optically preamplified PPM offers sensitivities significantly better than the fundamental limit of an optically preamplified PCM system and in fact approaches that of coherent detection.<<ETX>>

An optically preamplified intersatellite PPM receiver employing maximum likelihood detection

An original analysis, facilitated by the use of Gaussian approximation (GA) and Chernoff bound (CB) techniques, is presented for an optically preamplified intersatellite pulse position modulation (PPM) receiver employing maximum likelihood detection (MLD). The theoretical results, from calculations performed at a wavelength of 1.54 /spl mu/m and bit rate of 25 Mb/s demonstrate that the receiver is approximately 1.5 dB more sensitive than an earlier optically preamplified PPM receiver and also more sensitive than the fundamental limit of optically preamplified on-off keyed (OOK) NRZ signalling. Thus, it is demonstrated that the proposed receiver configuration is a strong contender for implementation in future laser intersatellite communication systems.

Timing Considerations for Optical Fibre PPM

Digital pulse position modulation (PPM) has been shown to be an effective modulation format for the optical fibre channel. It is paricularly attractive as it can exploit the abundant mom mode optical fibre bandwidth to offer improved performance. The format is a discrete time modu- lation format wherein synchronisation at both the slot and the fnme levels is vital. In this paper we derive an original analytic expression that predicts the spectral properties of optical fibre digital PPM on the basis of its cyclostationary random properties. We establish the conditions required to achieve both slot and frame synchronisation and further, we show that the system synchronisability can be optimised in terms of its parameters. In particular. we consider the effect of the pulse shape, modulation index and the data probability distribution on the spectral properties. Finally, we pre- sent original practical results measured on a 128-ary PPM system and show that they are within 1 dB of those predicted by our analytic model. We conclude that optical fibre digital PPM synchroni- sation can be achieved and further, optimised, in terms of the major system parameters.

Frame synchronisation for optical fibre digital PPM

An appropriate random variable is incorporated into an original model to represent the stochastic data sequence encoded. It is shown that unlike free space PPM, optical fibre exhibits a discrete component at the frame rate that can be used for synchronisation. The modulation index can be employed to enhance this component. Consideration is given to the nature of the dispersive optical fibre channel. Original practical results measured on an experimental system are shown to be in agreement with the theoretical predictions. The paper concludes by identifying a set of PPM parameters that optimises frame synchronisation.<<ETX>>

Theoretical characterisation and practical implementation of optical fibre PPM self synchronisation sequences

A novel technique for estimating the optical fibre PPM frame phase and eliminating the pattern dependent jitter is proposed while practical implementations and a mathematical characterisation for the technique are reported. Use is made of naturally occurring sequences thus avoiding the sensitivity and bit rate penalties associated with the previous methods. Tracking additional sequences is demonstrated and shown to be beneficial resulting in a frame rate discrete component enhancement of 10.8 dB and timing variance reduction from 12 × 10−3rad2 to 3.6 × 10−3rod2. Utilising the systematic jitter rejection method proposed resulted in a measured timing variance reduction from 3.6 × 10−3rad2 to 4.2 × 10−5rod2. The limit is imposed by the PLL performance while good correlation is depicted with the theoretical model.

Optically preamplified n-ary PPM systems

An analysis is presented for an optical fiber n-ary pulse position modulation (PPM) system employing optical preamplification. Calculations, performed at a bit-rate of 622 Mbit/s and a wavelength of 1.53 micrometers , demonstrate that the incorporation of an optical preamplifier leads to a sensitivity benefit of 13.3 dB compared to the non-preamplified case and a sensitivity improvement of 7.5 dB over an equivalent PCM system. Further, the work also shows that sensitivities approaching that of homodyne PSK PCM are potentially achievable.

Microstrip implementation of optimal pulse position modulation pre-detection filters

The optimum pre-detection filter for a PPM signal comprises a matched filter in cascade with a proportional-derivative-delay network. This paper addresses the problem of realising such a filter and in particular, describes a technique for synthesising the matched filter on microstrip.<<ETX>>

Implementation and performance considerations for a PPM correlator-synchroniser

An original implementation for a PPM correlator-synchroniser is reported. The PPM frame synchronisation is achieved on both the frequency and phase levels. The proposed technique does not suffer any of the limitations of the previous methods such as the bit rate and sensitivity penalties. Original theoretical and practical results are reported for the synchroniser while a performance evaluation is carried out. An original method for pattern dependency elimination is proposed, implemented and characterised.<<ETX>>

On the design of a jitter-tolerant synchronisation subsystem for optical fibre PPM

An optimum pre-synchronisation filtering strategy is proposed and analysed in the context of optical fibre pulse position modulation (PPM). Under Ideal synchronisation, the PPM system is shown to outperform the equivalent PCM system sensitivity. The PPM system performance penalty due to jitter is evaluated and an original expression is presented for the jittered PPM format power spectral density (PSD). The performance improvement obtained by using the proposed filtering is ascertained and the system parameters are specified for optimum performance.<<ETX>>

A programmable bursty traffic algorithm for use in packet-level discrete time packet switch simulation studies

A novel scheme for the classification and reproduction of packet channel burstiness is presented. Channels are described by burst-length-loading pairs, and an algorithm is presented which can faithfully reproduce any traffic characteristic for use in packet-level discrete time packet switch simulation studies.<<ETX>>